Piston



F. CLARK PISTON March 31, 1931.

Filed Oct. 14. 1929 the part of Patented Mar. 31, 1931 UNITED STATES PATENT OFFICE FRED CLARK, OF CLEAR LAKE-,MINNESOTA, ASSIGNOB TO MAE CLARK, OF CLEAR LAKE,

' MINNESOTA PISTON This invention relates to pistons for internal combustion engines and the like and has for some of its objects the provision of a light, relatively inexpensive piston having excellent wearing qualities. Another object is the provision of a piston in which the cylinder-engaging wearing surfaces thereof may be expanded to compensate for wear thereon and the cylinder wall. Still another object of the invention is the provision of a piston in which the cylinder-engaging sklrt portions thereof will, with use, expand automatically to an extent approximately equal to the combined wearing of the piston and cylinder wall and thereby maintain a snug fit between the piston skirt and cylinder within reasonable limits of wear without creating excessive friction therebetween. These and other objects will be more clearly brought out in the drawings, Specification and claims.

In the accompanying drawings, which il lustrate the invention, like characters indicate like parts throughout the several views.

Referring to the drawings:

Fig. 1 is a perspective view of the complete piston;

Fig. 2 is a section taken on the line 2-2 of Fi 1;

Fig. 3 is a section taken on the line 33 of Fig 2;

ig. 4. is a fragmentary enlarged section of certain parts shown in Fig. 2; and

Fig. 5 is aperspective view ofthe piston shoe expanding spring.

The numeral 6 indicates a piston of an internal combustion engine or the like as an en tirety, 7, the piston rings, 8, the connecting rod and 9, the connecting rod wrist pin. The skirt of the main body of the piston, that is, the piston below the. lowermost ring 7, is reduced intermediate its opposite extremities to form a shoe-receiving land 10 bordered by upper and lower circumferential shoulders 11 and 12. In'this land 10 are seated a pair of cylinder-engaging shoes 13 hich shoes are placed with their centers at diametrically opposite points, the axis of said centers being at right angles to the longitudinal axis of the wrist pin. These shoes ""13'eXteI1d. verticallyb'etween and seat against shoulders 11 and 12 at their upper and lowe portions, respectively, and are spaced apart at their opposite sides and spaced from the wrist pin openings in the piston body.

Interposed between each of the semi-cylindrical shoes 13 and the reduced skirt portion is a normally flat spring plate 14, preferably of approximately the same dimensions as the shoe 13. These spring members. 14 at all times exert a quite great outward pressure on the shoes and said shoes are adjustably held positioned against outward movement by machine screws or the like 15. The stems of the screws 15 have screw-threaded engagement with holes. 16 in the sides of the reduced,

skirt portion of the piston body and the heads 16 thereof are tapered or conical'in form and are countersunk in and engage the tapered sides of the holes 17 in the shoes 13. The shoes 13, spring plates 14:, and piston body 10 are thus held together by the screws 15 and by adjustment of the screws the shoes, which are always under tension of the springs 14 to be moved outward, may be adjustably moved inward or outward to compensate for wear on the shoes and cylinder wall after a long period of operation or to adapt the piston to fit cylinder walls varying several thousandths of an inch. In order that the screws 15 may have suflicient screw-threaded engagement with the piston body, said body is provided with internal bosses 18 into which the screws are extended.-

The horizontal centers of the shoes 13 are at right angles to the axis of the wrist pin and therefor also at right angles to the axis of-the engine crank shaft, therefore, it may be stated that the shoes are on the thrust sides of the piston. The shoes 13 are normally ad usted to extend slightly beyond the outermost portions of the piston body so that said shoes will-be the only parts of the complete piston except the rings to have frictional engagement with the cylinder walls.

It is, of course, understood that reciprocating pistons that are connected to a crank shaft are subject to side thrust due to the various angles of the connecting rod during rotation of the crank shaft. This thrust is xerted on, one side of the piston on its downward movement and on the other side thereof on its upward movement. This side thrust will have a tendency to cause the piston to rock slightly in the cylinder on the axis of the wrist pin and as the shoes 13 are only yieldingly held outward against the heads of the screws 15, by pressure of the spring plates 14, said shoes will, upon receiving such thrust, rock or move pivotally on the screw heads very slightly to conform with the sides of the cylinder wall. This slight rocking movement of the shoes 13 on the head of the screws 15 against the yielding action of the springs 14, will, to a considerable degree, e iminate or cushion slapping action of the piston against the cylinder wall and thereby quiet the engine and decrease the wear on the piston and cylinder wall.

The slight rocking or pivotal action of the shoes 13 on the heads 16 of the screws 15 will cause a wearing action to take place that will very gradually permit the spring plates 14 to move the shoes outward. This outward movement will, of course, be extremely gradual and will be dependent mainly upon the size of the screw head, and the degree of taper thereof and the tapered holes 17 in the shoes. By experiment, I have found that by providing the correct degree of taper and size of the screw head 16 and by using metals of the proper wearing qualities, the extent of outward movement of the shoes over a period of time may be approximately in proportion to the combined wear of the shoes 13 and cylinder wall. In this manner, the piston may be used over a very long period of time without taking the same out in order to adjust the screws 15. In some cases, I have found that the pivotal or rocking movement of the shoes on the screw heads 16 is so slight that the wear between the screw heads 16 and shoes is so slow that the outward movement of the shoes will be too slow to sufiiciently compensate for the wear of the shoes and cylinder. In such cases, however, I found that by cutting a multiplicity of slots 19 in the shoes and passin the same through the sides of the holes 17, the screw-engaging surface of the shoes may be decreased sufliciently to permit enough wear to allow sufiicient expanding action of the shoes.

This type of piston may be made of any suitable material but it has been found extremely practical to make the main body of the piston of a very light alloy and the shoes of cast iron or steel so as to provide a light piston haying excellent wearing qualities. It is understood that piston cylinders usually wear to a greater degree toward the top than they do toward the bottom due to the friction of the piston rings which are, of course, near the top of the piston. For this reason I have found it very practical to offset the screw 15 from the centers of the shoes 18,

longitudinal to the axis of the piston, in a. direction from said centers opposite the piston head so that said shoes will be permitted to move outward a greater distance at their.

upper or top portions than would be the case if said screws were located at or above the center of the shoes.

When this piston is used in badly worn cylinders the shoes will so adapt themselves to fit the taper of the cylinder wall that slapping of said pistons will be reduced to a minimum.

What I claim is:

1. In combination with an engine cylinder, a cylinder piston including a main piston body, a reduced skirt portion or land intermediate the top and bottom of the main piston body, diametrically opposed semicylindrical cylinder-engaging shoes set in said land, said shoes being spaced from the reduced sides of the skirt portion and normally extending beyond the outermost portions of the main piston body, yielding pressure means between said shoes and the reduced sides of the skirt tending to move the shoes outward, and means acting against the yielding pressure means for a predetermined clearance between said shoes and cylinder wall but allowing said shoes to rock pivotally thereon.

2. In combination with an engine cylinder, a cylinder piston including a main piston body, a reduced skirt ortion intermediate the top and bottom of said piston body, a semi-cylindrical cylinder engaging shoe set in said reduced skirt portion, said shoe being spaced from the reduced skirt portion of said piston body and normally extending beyond the outermost portion of said main piston body, yielding pressure means between said shoe and the reduced skirt portion tending to move the shoe outward, and means acting against the yielding pressure means for maintaining predetermined clearance between said shoe and the cylinder wall,

said means being so arranged as to permit 5% very gradual outward movement of said shoe to a degree approximately in proportion to the wear between the piston and cylinder wall and thereby approximately maintain a desired clearance between said piston and cylinder wall, said means that acts against the yielding pressure means'being in the form of a screw passed through the shoe and having screw-threaded engagement in the piston body and the head thereof being tapered or conical in form and counter-sunk in a tapered hole in the shoe below the outer surface of said shoe, the outward movement of the shoe caused by slight rock ing movement being due to wear between the tapered screw head and the co-operating tapered hole in the shoe and the amount of wear which takes place and consequently the extent to which the shoe will be permitted maintaining I reduced sides of the skirt portion and normally extending beyond the outermost portions of the main piston body, yielding pressure means between said shoes and the reduced sides of the skirt tending to move the shoes outward, and means acting against the yielding predetermined clearance between said shoes and-cylinder wall, and said means being so arranged as to permit very gradual outward movement of the shoes to a degree approximately in proportion to the wear between the shoes and cylinder wall and thereby approximately maintaining the desired clearance between the shoes and cylinder, said means that acts against the yielding pressure means for maintaining a predetermined clearance between the shoes and cylinder wall being oifset from the centers of said shoes longitudinal to the axis of the piston in a direction opposite tovthe head of said piston.

4'. In combination with an engine cylinder, a cylinder piston including a main piston body, a reduced skirt portion intermediate the top and bottom of the main piston body, a semi-cylindrical cylinder-engaging shoe set in said reduced skirt portion, said shoe being spaced from the reduced sides of the skirt por-. tion and normally extending beyond the outermost portions of the main piston body, yielding pressure means between said shoe and the reduced side of the skirt tending to move the said shoe outward, and means acting against the yielding pressure means for maintaining a predetermined clearance between said shoe and cylinder wallbut allowing said shoe to rock pivotally thereon.

5. In combination with an engine cylinder, a cylinder piston including a main piston body, a reduced skirt portion or land intermediate the top and bottom of the main piston body, diametrically opposed semi-cylindrical cylinder-engaging shoes set in said land, said shoes being-spaced from the reduced sides of the skirt portion and normally extending beyond the outermost portions of the main piston body, yielding pressure means between said shoes and the reduced sides of the skirt tendingto move the shoes outward,

and means acting against the yielding pressure means for maintaining a predetermined clearance between said shoes and cylinder to permit very gradual outward movement wall, and said means being so arranged as pressure means for maintaining a.

tween the shoe low the'outer surface of-said shoes, the outward movement of the shoes caused by slight rocking action being due to wear between the tapered screw head and the co-operating tapered hole in the shoes and the amount of wear which takes place and consequently the extent to which the shoes will be permitted, to

move outward with use being dependent in part upon the size of the head and the degree of taper thereof.

- '6. In combination with an engine cylinder, a cylinder piston including a. main piston body, a reduced skirt ortion' intermediate the top and bottom of t e main piston body, a semi-cylindrical cylinder-engaging shoe set in said reduced skirt portion, said shoe being spaced from the reduced side of the skirt portion and normallyv extending beyond the outermost portion of the main piston body, yielding pressure means between said shoe and the reduced sides of the skirt tending to move the shoe outward, and means acting against the yielding pressure means for maintaining a; predetermined clearance between said shoe and cylinder wall, and said means being so arranged as to permit very gradual outward movement of the shoe to a degree approximately in proportion to the wear beand cylinder wall and thereby approximately maintaining thedesired clearance between the shoes and cylinder, said means that acts against the yielding pres-' sure means for maintaining a predetermined clearance between theshoe and cylinder wall being offset from the centers of said shoe longitudinal to the axis of the piston in a direction opposite to the head of said piston.

7. In combination with a cylinder, a cylinder piston having cylinder-engaging surfaces and means controlled by the action of the piston in the cylinder operative'to maintain approximately a predetermined desired clearance between said cylinder and certain cylinder-engaging surfaces of the piston to compensate for piston and cylinder wear.

In testimony whereof I affix my signature. FEED CLARK. 

